Horizontal deflection circuit

ABSTRACT

A horizontal deflection circuit capable of performing various corrections. It is characterized by grounding one end of a first parallel circuit connecting a first switching element  11 , a first damper diode  12 , and a first resonance capacitor  13  in parallel, connecting the other end of the first parallel circuit to one end of a second parallel circuit connecting a second switching element  21 , a second damper diode  22 , and a second resonance capacitor  23  in parallel, and further connecting the other end of this first parallel circuit to a direct-current power source terminal through a primary winding of a flyback transformer  6 , grounding the other end of this second parallel circuit through a series circuit of a horizontal deflection coil  4  and an S-curve correction capacitor  5 , grounding the connection middle point of the horizontal deflection coil  4  and S-curve correction capacitor  5  through a parallel circuit of an intermediate pincushion distortion correction circuit  60  and a horizontal linearity correction circuit  70 , and installing switching element control means  40  for switching the first switching element  11  by a horizontal drive signal, and controlling the OFF start timing and OFF period of the second switching element  21.

TECHNICAL FIELD

The present invention relates to a horizontal deflection circuit used ina television receiver or a display device using a cathode-ray tube(CRT), and more particularly to a horizontal deflection circuit capableof correcting pincushion distortion or adjusting the screen size in thehorizontal direction.

BACKGROUND ART

For example, in a television receiver, in order to correct pincushiondistortion, it is known to use a diode modulation circuit in ahorizontal deflection circuit.

In the diode modulation circuit, the damper diode of the horizontaldeflection circuit is composed of two diodes connected in series, and apincushion modulation coil is connected in series to a horizontaldeflection coil, and the connection middle point of two diodes and theconnection middle point of the horizontal deflection coil and pincushionmodulation coil are connected through an S-curve correction capacitor.To the diode at the side connected parallel to the pincushion modulationcoil, a switching element for correction of pincushion distortion isconnected in parallel.

This switching element for correction of pincushion distortion issynchronized with the horizontal pulse, and is turned on in the latterhalf of the retrace interval of horizontal deflection. The width of thisON period is modulated parabolically in the vertical period. By thuschanging the width of the ON period of the switching element forcorrection of pincushion distortion, the quantity of deflection currentdistributed from the horizontal deflection coil into the pincushionmodulation coil changes periodically, and the deflection current ismodulated parabolically in the vertical period, and the pincushiondistortion is corrected.

At the same time, since the current flowing in the S-curve correctioncapacitor is also modulated parabolically in the vertical period, theS-curve correction is also changed in the vertical period, and issmaller in the top and bottom of the screen and large in the center, sothat the intermediate pincushion distortion is also corrected.

In the horizontal deflection circuit having such diode modulationcircuit, in order to correct the horizontal linearity distortion causeddue to presence of internal resistance of the horizontal deflectioncoil, it is known to connect a horizontal linearity correction coilcomposed of a magnetically biased saturable reactor in series to thehorizontal deflection coil.

When using such diode modulation circuit for correcting pincushiondistortion, a sufficiently large correction amount of pincushiondistortion is obtained as compared with the conventional pincushiondistortion correction circuit using saturable reactor, and therefore itis used in the television receiver or display device using a wide-angleCRT requiring a large correction amount, in particular.

However, a problem occurs when the horizontal deflection circuit usingsuch diode modulation circuit is applied in the television receiver orthe like of progressive scanning system, that is, the double speedscanning system coming into use recently. This problem is describedbelow.

In the television receiver of progressive scanning system, since thehorizontal deflection frequency is two times as high as that of theordinary scanning system, that is, interlaced scanning system, theretrace interval of the horizontal deflection current is ½. Consideringthe dielectric strength of the switching element for horizontal output,if the voltage of the retrace pulse is not changed, the maximumamplitude of the horizontal deflection current must be doubled.Accordingly, a switching element of a large capacity is needed, thecircuit cost is raised, and the power consumption of the switchingelement and its peripheral elements is increased.

It is hence desired to employ the horizontal deflection circuit usingsuch diode modulation circuit in the television receiver or the like ofdouble speed scanning system without increasing the power consumption.

Previously, the present applicant proposed, as a horizontal deflectioncircuit for use in a television receiving using a CRT, a horizontaldeflection circuit capable of applying a voltage of about 2 kv to thehorizontal deflection coil by using two switching elements, and savingthe power consumption and reducing the cost substantially by regulatingthe horizontal deflection current of the television receiver scanning atdouble speed to the level of an ordinary television receiver in JapanesePatent Application No. 9-221366 (U.S. patent application Ser. No.133,992).

In this proposed horizontal deflection circuit, one end of a parallelcircuit of a first switching element, a first damper diode, and a firstresonance capacitor is grounded, and one end of a parallel circuit of asecond switching element, a second damper diode, and a second resonancecapacitor, and one end of a primary winding coil of a flybacktransformer are connected to other end of the first switching element, adirect-current voltage is supplied to this connection point through theprimary winding coil of the flyback transformer, a horizontal deflectioncoil is connected to other end of the second switching element, anS-curve correction capacitor is connected in series to the horizontaldeflection coil, and the other end of the S-curve correction capacitoris grounded, and further switching element control means for controllingthe OFF start timing and OFF period of the second switching element isprovided.

According to this proposed horizontal deflection circuit, the withstandvoltage of the switching element for horizontal output may be low, andthe retrace pulse voltage applied to the horizontal deflection coil islarge and the deflection current is small, so that the power loss of thedeflection system is decreased, and moreover screen size adjustment inthe horizontal direction and distortion correction can be done easily.

However, in the horizontal deflection circuit proposed in JapanesePatent Application No. 9-221366, although the S-curve is corrected bythe S-curve correction capacitor connected in series to the horizontaldeflection coil, the correction amount is not changed, and therefore theintermediate pincushion distortion is not corrected.

To correct the intermediate pincushion distortion, it may be consideredto employ a diode modulation system, but since the circuit type isdifferent, intermediate pincushion distortion cannot be corrected by thesame method.

Similarly, in the horizontal linearity correction, in the proposedhorizontal deflection circuit, since it is different from the horizontaldeflection circuit of diode modulation system, horizontal linearitytransformer cannot be used, and pincushion imbalance occurs between theright and left side of the screen.

Besides, when the horizontal linearity correction coil or horizontallinearity correction transformer is used, the voltage at both endsapplied to the horizontal deflection coil is decreased by the portion ofthe voltage at both ends applied to the coil. As a result, the capacityand efficiency of the power source cannot be fully utilized, which maylead to problems of increase of power consumption and generation ofheat.

Therefore, if the horizontal linearity can be corrected by using aswitching element, it is not only advantageous for power consumption,but also easy for control of correction characteristic and possible tolower the cost. It is hence desired to realize a horizontal deflectioncircuit capable of correcting horizontal linearity by using a switchingelement.

In the light of the background discussed above, it is an object of theinvention to correct intermediate pincushion distortion, horizontallinearity and others as efficiently as in the horizontal deflectioncircuit of the conventional diode modulation system, in a horizontaldeflection circuit using two switching elements, capable of applying avoltage of about 2 kV to the horizontal deflection coil, regulating thehorizontal deflection current of scanning at double speed at a level ofan ordinary horizontal deflection circuit, saving the power consumption,and lowering the cost substantially.

It is also an object of the invention to keep constant the high voltagedirect-current voltage obtained from the secondary winding of theflyback transformer, even in the case of such corrections.

DISCLOSURE OF THE INVENTION

A horizontal deflection circuit of the present invention ischaracterized by grounding one end of a first parallel circuitconnecting a first switching element, a first damper diode, and a firstresonance capacitor in parallel, connecting other end of the firstparallel circuit to one end of a second parallel circuit connecting asecond switching element, a second damper diode, and a second resonancecapacitor in parallel, and further connecting the connection point ofother end of the first parallel circuit and one end of the secondparallel circuit to a direct-current power source through a primarywinding of a flyback transformer, grounding the other end of the secondparallel circuit through a series circuit of a horizontal deflectioncoil and an S-curve correction capacitor, grounding the connectionmiddle point of the horizontal deflection coil and S-curve correctioncapacitor through a parallel circuit of an intermediate pincushiondistortion correction circuit and a horizontal linearity correctioncircuit, and installing switching element control means for switchingthe first switching element by a horizontal drive signal, andcontrolling the OFF start timing and OFF period of the second switchingelement.

According to the present invention, since the circuit is composed so asto ground the S-curve correction capacitor connected in series to thehorizontal deflection coil, it is easy to correct various deflectionsystems connecting a specified circuit element or a specified circuitbetween this S-curve correction capacitor and the ground.

Accordingly, connecting in parallel to the S-curve correction capacitor,by assembling an intermediate pincushion distortion correction circuitand a horizontal linearity correction circuit, a voltage for correctioncan be superposed at both ends of the S-curve correction capacitor, andthe voltage at both ends of the horizontal deflection coil can bevaried, so that various deflection systems can be corrected.

The invention also presents a horizontal deflection circuit which ischaracterized by grounding one end of a first parallel circuitconnecting a first switching element, a first damper diode, and a firstresonance capacitor in parallel, connecting the other end of the firstparallel circuit to one end of a second parallel circuit connecting asecond switching element, a second damper diode, and a second resonancecapacitor in parallel, and further connecting the connection point ofother end of the first parallel circuit and one end of the secondparallel circuit to a direct-current power source through a primarywinding of a flyback transformer, grounding the other end of the secondparallel circuit through a series circuit of a horizontal deflectioncoil and an S-curve correction capacitor, and installing switchingelement control means for switching the first switching element by ahorizontal drive signal, and controlling the OFF start timing and OFFperiod of the second switching element, in which capacity varying meansfor varying the capacity of the first resonance capacitor is alsoprovided to keep constant the high voltage generated by the flybacktransformer by varying the capacity of the first resonance capacitor ina horizontal retrace interval.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a structural diagram showing a first embodiment of ahorizontal deflection circuit of the invention.

FIG. 2 is a line diagram for explaining the intermediate pincushiondistortion correction in the horizontal deflection circuit shown in FIG.1.

FIG. 3 is a line diagram for explaining the horizontal linearitycorrection in the horizontal deflection circuit shown in FIG. 1.

FIG. 4 is a waveform diagram for explaining a basic horizontaldeflection operation in the horizontal deflection circuit shown in FIG.1.

FIG. 5 is an equivalent circuit diagram for explaining a basichorizontal deflection operation in the horizontal deflection circuitshown in FIG. 1.

FIG. 6 is a structural diagram showing a second embodiment of ahorizontal deflection circuit of the invention.

FIG. 7 is a wiring diagram showing a specific example of the horizontaldeflection circuit shown in FIG. 6.

FIG. 8 is a structural diagram showing a third embodiment of ahorizontal deflection circuit of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

A first embodiment of a horizontal deflection circuit of the inventionis described below while referring to FIG. 1 to FIG. 5.

As shown in FIG. 1, the horizontal deflection circuit in the firstembodiment is composed of a parallel circuit of a switching element 11for horizontal output, a damper diode 12, and a resonance capacitor 13,and a parallel circuit of a switching element 21, a damper diode 22, anda resonance capacitor 23, which are connected in series, in which apower source is supplied to this connection point through a primarywinding of a flyback transformer 6. The end of the opposite side of theconnection point of the switching element 11 is grounded, the end of theopposite side of the connection point of the switching element 21 isconnected to a horizontal deflection coil 4, one end of an S-curvecorrection capacitor 5 is connected in series to this horizontaldeflection coil, and other end of the S-curve correction capacitor isgrounded.

This horizontal deflection circuit comprises pulse reading circuits 17,27 for reading the voltage at both ends of the switching elements 11,21, and a switching element control circuit 40 for controlling on/off ofthe switching element 21 by operating on the basis of this voltage.

The operation of this circuit is explained below while referring to FIG.1, FIG. 4, and FIG. 5.

In FIG. 1, a horizontal drive signal is fed into the switching element11 for horizontal output, and the switching element 11 for horizontaloutput is turned on. At the same time, the switching element 21 is alsoturned on by a drive signal from the switching element control circuit40, and the both are set in conductive state, and a deflection currentflows in the horizontal deflection coil 4. By contrast, when turningoff, the switching element 11 is driven to be turned off ahead of theswitching element 21, and the retrace interval (horizontal retraceinterval) begins. In this retrace interval, the switching element 21 iscontrolled to be turned on or off by the switching element controlcircuit 40. The series of operations is explained below by dividing thehorizontal deflection period and using an equivalent circuit.

<Trace Interval (a)>

The trace interval (a) is the conductive period of both switchingelements 11 and 21, and the equivalent circuit is as shown in FIG. 5A,which is same as the constitution of the horizontal deflection circuitcomposed of one stage of switching element known hitherto. At this time,both deflection current and flyback transformer current increase at aninclination corresponding to the voltage at both ends of the S-curvecorrection capacitor 5 and supply voltage, respectively. The waveform ofdeflection current at this time is shown in FIG. 4D.

<Initial Phase of Retrace Interval>

When getting into the retrace interval, first the switching element 11is turned off by a horizontal drive signal. At this time, the switchingelement 21 is still conductive, and the equivalent circuit becomes asshown in FIG. 5B, which is same as an ordinary horizontal deflectioncircuit. At this time, the current flowing into the flyback transformer6 and horizontal deflection coil 4 begins to flow into the resonancecapacitor 13, and a voltage is generated at both ends of the resonancecapacitor 13, and the current begins to be inverted by it. That is, theresonance operation starts, and the voltage and current waveform is thewaveform shown in interval (b) in FIG. 4.

<OFF Period of Switching Element 21 in Retrace Interval>

After the deflection current has reached 0 in the latter half of theretrace interval, if the switching element 21 is turned off, theequivalent circuit remains same as in FIG. 5B and no change occursbecause of the presence of the damper diode 22, but when the switchingelement 21 is turned off 21 before the deflection current reaches 0 inthe first half of the retrace period, the equivalent circuit is changedas shown in FIG. 5C, and another resonance capacitor 23 is connected inseries to the horizontal deflection coil 4.

The deflection current also flows into the resonance capacitor 23, and avoltage is generated at both ends of the resonance capacitor 23, andtherefore a pulse voltage larger than the pulse at both ends of theswitching element 11 can be applied at both ends of the horizontaldeflection coil 4 (see FIG. 4A).

Herein, the peak value of the retrace pulse voltage at both ends of theswitching element 11 is mainly determined by the supply voltage andratio of retrace time and trace time, and this pulse (see FIG. 4B) canbe boosted by the flyback transformer 6 (only primary winding shown) toa high voltage to be used in the CRT.

<Latter Half of Retrace Interval>

The retrace interval is terminated when all the electric charge onceflowing into the resonance capacitors 13, 23 flows out and the voltageat both ends becomes 0, and the damper diode conducts automatically (thediode is shown as an ideal diode for the sake of simplicity).

Herein, the since the current flowing into the resonance capacitor 23 isalways smaller than the current flowing into the resonance capacitor 13,the electric charge is used up earlier in the resonance capacitor 23,and the damper diode 22 conducts ahead of the damper diode 12.Therefore, the pulse generated at both ends of the switching element 21is narrower in the pulse width as compared with the pulse generated atboth ends of the switching element 11 (see interval (c) in FIG. 4B andFIG. 4C).

Further, when the OFF timing of the switching element 21 is delayed, thecurrent flowing into the resonance capacitor 23 is much smaller, and thepulse at both ends of the switching element 21 at this time is furthernarrower in the pulse width, and the pulse height is lower. That is, bycontrolling the phase of OFF timing of the switching element 21, theretrace pulse voltage applied to both ends of the horizontal deflectioncoil 4 can be controlled, so that the amplitude of the deflectioncurrent can be varied.

In FIG. 4, interval (d) is same as interval (b) in equivalent circuit,and its explanation is omitted.

<Trace Interval (e)>

When the damper diode 22 thus conducts, the circuit returns to theequivalent circuit in FIG. 5B, and the retrace operation continues sameas in the ordinary deflection circuit until the voltage at both ends ofthe resonance capacitor 13 becomes 0, and at the end of retrace, itreturns to the equivalent circuit in FIG. 5A, and the trace interval (e)starts. In this trace interval (e), a horizontal deflection currentflows from the horizontal deflection circuit 4 in the forward directionof the damper diodes 12, 22 (see FIG. 4D). In this period, the switchingelements 11, 21 are set in conductive state to be ready for next traceinterval (a).

In this way, the horizontal deflection current repeats the deflectionintervals (a), (b), (c), (d), and (e), and the horizontal deflectioncoil 4 forms a horizontal deflection magnetic field.

Next, the method of varying the amplitude of the horizontal deflectioncurrent by controlling the OFF timing of the switching element, andadjusting the pincushion distortion and the horizontal screen size isexplained in detail below.

The maximum amplitude (PP value) Ipp of the horizontal deflectioncurrent is proportional to the integral value of the retrace pulsevoltage applied to both ends of the horizontal deflection coil in theretrace interval. This retrace pulse voltage is about 1200 to 2200volts, and it is divided into a low voltage that can be processed, andthis voltage and the reference voltage expressing the amplitude of thehorizontal deflection are compared, and the difference is integrated,and by feeding back to the drive signal of the switching element so thatthis integral value may be 0, thereby controlling the Ipp of thehorizontal deflection current at high precision.

In the example shown in FIG. 1, retrace pulse voltages applied to theswitching elements 11, 21 are detected respectively by the pulse readingcircuits 17, 27. The detected voltage is obtained by dividing theretrace pulse voltage by capacitor or the like. The detected voltage isfed into the switching element control circuit 40, and the retrace pulsevoltage (divided voltage) of the switching element 21 is subtracted fromthe retrace pulse voltage (divided voltage) of the switching element 11by using a subtractor 41 such as operational amplifier. Thisdifferential voltage and the amplitude control voltage corresponding tothe specified horizontal amplitude are compared in a comparator 42. Thisamplitude control voltage usually contains a parabolic voltage forcorrecting the pincushion distortion.

The compared voltages are integrated by an integrator 43 to be adirect-current voltage, which is fed into a phase regulator 44 as asignal for adjusting the phase (OFF timing) of the drive signal of theswitching element 21. The timing pulse formed in the phase regulator 44forms a drive signal sufficient for driving the switching element 21, ina drive waveform generator 45. By such feedback loop, the switchingelement 21 produces a deflection current while controlling the OFFtiming.

The explanation so far relates to the operation when the closed loopcontrol system of OFF timing is in a stable operation state, butdepending on the circuit constitution, it must be noted that theoperation may be different in a transient period, such as startingmoment when the power source is turned on.

In the control system shown in FIG. 1, the area of subtracting thevoltage waveform (divided voltage) of the retrace pulse of the switchingelement 21 from the voltage waveform (divided voltage) of the retracepulse of the switching element 11 changes linearly with respect to theamplitude of the deflection current. When the power source is turned on,the feedback loop is active so that retrace pulse may not be generatedat both ends of the switching element 21 until the differential areareaches a specific size. In other words, retrace pulse is not generatedat both ends of the switching element 21 until the retrace pulse at bothends of the switching element 11 reaches a specified wave crest value,so that stable starting is realized.

In this embodiment, as shown in FIG. 1, the connection middle point ofthe horizontal deflection coil 4 and S-curve correction capacitor 5 isgrounded through a parallel circuit of an intermediate pincushioncorrection circuit 60 and a horizontal linearity correction circuit 70.

In this case, when resonating by connecting the S-curve correctioncapacitor 5 in series to the horizontal deflection coil 4 as shown inFIG. 1, the voltage at both ends of the S-curve capacitor 5 draws acurve as shown in FIG. 3B. This sinusoidal voltage component issuperposed, the deflection current increases in the central area of thescreen, and decreases in the peripheral area, so that the S-curve may becorrected. Therefore, by changing the voltage at both ends of theS-curve correction capacitor 5 as shown in FIG. 3B dynamically in thevertical scanning period, the intermediate pincushion distortion can becorrected.

This intermediate pincushion distortion correction circuit 60 iscomposed, for example as shown in FIG. 2A, by connecting a seriescircuit of a capacitor 62 and a switching element 61 in parallel to theS-curve correction capacitor 5. By turning off this switching element 61in the first half of the horizontal scanning period, the capacity of theS-curve correction capacitor can be changed over between the right andleft part of the screen and the central part of the screen, therebychanging the amount of S-curve correction. That is, it is corrected by aparallel circuit of S-curve correction capacitor 5 and capacitor 62 inthe right and left part of the screen, and corrected by the S-curvecorrection capacitor 5 only in the central part of the screen.

By modulating the switching timing of the switching element 61, the modeof correction of intermediate pincushion distortion is explained byreferring to FIG. 2B, FIG. 2C, and FIG. 2D. In a switching signal inputterminal 61 a of the switching element 61, a drive signal modulated inpulse width in vertical scanning period is fed. At this time, in theupper and lower part of the screen in the vertical direction, the OFFtiming of switching is delayed, while the OFF timing of switching isadvanced in the central part of the screen in the vertical direction.Accordingly, in the central part of the screen in the verticaldirection, the switching OFF timing is earlier, and the correction timeby the S-curve correction capacitor 5 only is longer, and the S-curvecorrection amount increases. To the contrary, in the upper and lowerpart of the screen in the vertical direction, the correction amount issmaller, and the correction amount in the vertical scanning period canbe changed dynamically, so that the intermediate pincushion distortioncan be corrected.

The horizontal linearity correction circuit 70 is composed as shown inFIG. 3A, in which the connection middle point of a capacitor 72connected in series to the horizontal deflection coil 4 and S-curvecorrection coil 5 is grounded through a series circuit of adirect-current blocking capacitor 73 and a switching element 71, and theconnection middle point of the capacitor 73 and switching element 71 isconnected to a direct-current power source terminal through a choke coil74. The operation of this horizontal linearity correction circuit 70turns off the switching element 71 in the horizontal scanning period,and turns on the switching element 71 in the retrace interval.

The horizontal deflection current is flowing by using the power sourceof the S-curve correction capacitor 5 in the scanning interval, andthere is a proportional relation between the change rate of thehorizontal deflection current and the voltage at both ends of theS-curve correction capacitor 5. Accordingly, while the deflectioncurrent is attenuating in the latter half of the scanning interval, thevoltage at both ends of the S-curve correction capacitor 5 is alsoattenuated in the latter half of the scanning interval (dotted line inFIG. 3D). In the retrace interval, when the switching element 71 isturned on by the switching signal as shown in FIG. 3C, the current flowsfrom the S-curve correction capacitor 5 through the switching element71, and the voltage at both ends decreases. As a result, the risingtiming of the voltage at both ends of the S-curve correction capacitor 5is delayed, and the voltage at both ends decreases in the first half ofthe scanning period, whereas the voltage at both ends is elevated in thelatter half (solid line in FIG. 3D).

When the ON time of this switching element 71 is longer, thecorresponding current flows more from the S-curve correction capacitor 5through the switching element 71, and the rising timing of the voltageat both ends of the S-curve correction capacitor 5 is further delayed,and the correction amount can be increased. Therefore, by modulating theON time of switching in the vertical scanning period, the horizontallinearity correction amount can be changed in the vertical scanningperiod.

The intermediate pincushion distortion correction circuit 60 andhorizontal linearity correction circuit 70 are not limited to theillustrated example alone. In parallel to the S-curve correctioncapacitor 5, various correction circuits can be incorporated, and thevoltage for correction can be superposed at both ends of the S-curvecorrection capacitor, so that various deflection systems can becorrected easily. It is mostly because the circuit type in FIG. 1 isconstituted by connecting the S-curve correction capacitor 5 connectedin series to the horizontal deflection coil.

A second embodiment of a horizontal deflection circuit of the inventionis described by referring to FIG. 6 and FIG. 7. In FIG. 6 and FIG. 7,same parts corresponding to FIG. 1 are identified with same referencenumerals, and the detailed description is omitted.

As shown in FIG. 6, in the horizontal deflection circuit of the secondembodiment, one end of a first parallel circuit connecting a switchingelement 11 for horizontal output, a damper diode 12 and a variableresonance capacitor 50 in parallel is grounded, other end of this firstparallel circuit is connected to one end of a second parallel circuitconnecting a switching element 21, a damper diode 22, and a resonancecapacitor 23 in parallel, and a power source is supplied to thisconnection point through a primary winding 6 a of a flyback transformer6. At other end of this second parallel circuit, a horizontal deflectioncoil 4 is connected, and one end of an S-curve correction capacitor 5 isconnected in series to this horizontal deflection coil 4, while otherend of the S-curve correction capacitor 5 is grounded.

This horizontal deflection circuit comprises pulse reading circuits 17,27 for reading the terminal voltage of the switching elements 11, 21,and a switching element control circuit 40 for controlling on/off of theswitching element 21 by operating as specified on the basis of thisvoltage.

In the variable resonance capacitor 50 of this embodiment, as shownspecifically in FIG. 7, two capacitors 50 a and 50 b of specifiedcapacity are connected in series, and the connection middle point of thecapacitors 50 a and 50 b is grounded through a switching element 50 c,and this switching element 50 c is controlled as described below, thecapacity of the variable resonance capacitor 50 is varied in thehorizontal retrace interval, and therefore the high voltagedirect-current voltage obtained from the secondary winding 6 b of theflyback transformer 6 may be kept constant.

A high voltage detected voltage corresponding to the high voltagedirect-current voltage obtained at the secondary winding 6 b side of theflyback transformer 6 is supplied to one input terminal of an erroramplifier 51, while a reference voltage Vrf is supplied into other inputterminal from a reference voltage input terminal 51 a, and the highvoltage detected voltage and reference voltage Vrf are compared in theerror amplifier 51, and when the high voltage detected voltage exceedsthe reference voltage Vrf, the control signal is supplied into thisswitching element 50 c through a resonance capacitor capacity controlcircuit 52.

That is, in the example shown in FIG. 6, the voltage corresponding tothe high voltage direct-current voltage obtained at the secondarywinding 6 b side of the flyback transformer 6 is detected by resistancedivision, and this high voltage detected voltage is compared with thepredetermined reference voltage Vrf in the error amplifier 51, and it isdesigned to feed back so as to increase the capacity of the variableresonance capacitor 50 when this high voltage detected voltage exceedsthe reference voltage Vrf.

In this manner, change of high voltage direct-current voltage due tofluctuations of screen size, and fluctuations of high voltagedirect-current voltage due to brightness of the screen can besuppressed.

A specific structural example of the circuit diagram shown in FIG. 6 isgiven in FIG. 7. The variable resonance capacitor 50 shown in FIG. 7 iscomposed, as describe above, by connecting two capacitors 50 a and 50 bin series, conducting both ends of the capacitor 50 b at the groundingside in the horizontal retrace interval by the switching element 50 c,and the capacity of the resonance capacitor 50 in this horizontalretrace interval is changed over in binary system.

In the example shown in FIG. 7, the average capacity in the horizontalretrace interval can be varied before and after the period in thehorizontal retrace interval of OFF timing of the switching element 50 c,and the variable resonance capacitor 50 is formed equivalently.

That is, when the OFF timing is late, the capacity is largeequivalently, and the OFF timing is early, the capacity is smallequivalently.

This OFF timing is determined by comparison between the sawtooth wavegenerated by a sawtooth wave generating circuit 32 a composing theresonance capacitor capacity control circuit 52 in FIG. 7 and thedirect-current output of the error amplifier 51 in the comparator 52 b.

Thus, when the high voltage direct-current voltage supplied to the anodeof the CRT is raised, and the high voltage detection voltage of the highvoltage direct-current voltage obtained from the secondary winding 6 bof the flyback transformer 6 exceeds the reference voltage Vrf, theoutput direct-current voltage of the error amplifier 51 climbs up, andthe capacity of the variable resonance capacitor 50 is increasedequivalently, and the wave crest value of the horizontal retrace pulseis lowered, finally forming a feedback loop for lowering the highvoltage direct-current voltage supplied to the anode of the CRT.

If the high voltage direct-current voltage obtained at the secondarywinding side 6 b of the flyback transformer 6 is lowered, the feedbackloop is inverted in the high-low voltage relation.

The operation of the horizontal deflection circuit shown in FIG. 6 isexplained below, and the basis deflection operation is same as theoperation of the horizontal deflection circuit shown in FIG. 1, and theexplanation is omitted. However, in the horizontal deflection circuitshown in FIG. 1, the resonance capacitor 13 of fixed capacity is used,whereas the variable resonance capacitor 50 is used in the horizontaldeflection circuit shown in FIG. 6.

Similarly, the operation of varying the amplitude of the horizontaldeflection current by controlling the OFF timing of the switchingelement and adjusting the pincushion distortion and the horizontalscreen size is same as the operation of the horizontal deflectioncircuit shown in FIG. 1, and its explanation is also omitted.

In the horizontal deflection circuit shown in FIG. 6, the high voltagedetection voltage in the horizontal retrace period of the high voltagedirect-current voltage obtained from the secondary winding 6 b side ofthe flyback transformer 6 and the reference voltage Vrf are compared,and when the high voltage detected voltage exceeds the reference voltageVrf, feedback is applied so that the capacity of this variable resonancecapacitor 50 may be large, and therefore change of high voltagedirect-current voltage due to fluctuations of screen size andfluctuations of high voltage direct-current voltage due to brightness ofthe screen can be suppressed, so that the high voltage direct-currentvoltage can be stabilized.

FIG. 8 shows a third embodiment of a horizontal deflection circuit ofthe present invention. The circuit shown in FIG. 8 is described below,and the parts corresponding to the circuit shown in FIG. 6 areidentified with same reference numerals, detailed description isomitted.

The circuit shown in FIG. 8 is to control the capacity of the variableresonance capacitor 50 of the circuit shown in FIG. 6 so as to keepconstant the pulse width generated in the horizontal retrace interval atboth ends of the variable resonance capacitor 50.

That is, in the circuit shown in FIG. 8, the voltage of the pulsegenerated at both ends of the switching element 11 is read by a pulsereading circuit 17, and the detected rectangular pulse having a pulsewidth corresponding to the voltage of this pulse is shaped in a pulsewidth rectangular wave generating circuit 80, and a predeterminedreference specific width rectangular wave is formed in a specific widthrectangular wave generating circuit 81, and the detected rectangularwave and the specific width rectangular wave are supplied into asubtractor 82 and compared. When the width of the detected rectangularwave is smaller than the width of the specific width rectangular wave,the control signal from the subtractor 82 is supplied into the variableresonance capacitor 50 through the amplifier 83 and the variablecapacitor capacity control circuit 84, and feedback is applied so as toincrease the capacity of the variable resonance capacitor 50, and thepulse width generated in the horizontal retrace interval at both ends ofthe variable resonance capacitor 50 is kept constant.

In the example shown in FIG. 8, the other parts operate same as in theexample shown in FIG. 6.

The horizontal deflection circuit shown in FIG. 8 is similar to thehorizontal deflection circuit shown in FIG. 6 in its horizontaldeflection operation, and the pulse width generated at both ends of thevariable resonance capacitor 50, that is, in the horizontal retraceinterval obtained in the flyback transformer 6 is kept constant, so thatchange of high voltage direct-current voltage due to fluctuations ofscreen size can be suppressed.

The present invention is not limited to the above examples only, but maybe changed and modified within the scope of the invention.

According to the present invention, as described herein, using twoswitching elements, a voltage of about 2 kV can be applied to thehorizontal deflection coil, and the horizontal deflection current ofdouble speed scanning is regulated to the level of normal scanning, sothat the power consumption is saved and the cost is loweredsubstantially in the horizontal deflection circuit, which is providedwith the intermediate pincushion distortion correction circuit andhorizontal linearity correction circuit, so that various correctionssame as in the horizontal deflection circuit of the conventional diodemodulation system may be realized.

Also according to the present invention, as compared with the case ofusing the horizontal linearity correction coil, the voltage applied tothe horizontal deflection coil may be larger, and therefore the powerconsumption is saved and heat generation is suppressed, and moreoversince the linearity characteristic can be corrected by switchingoperation, the adjustments are easy, and the cost is lower than the casewhen correcting by using the coil.

Moreover, the invention is capable of suppressing and stabilizing thechanges of high voltage direct-current voltage supplied to the anode ofthe CRT.

What is claimed is:
 1. A horizontal deflection circuit characterized by:grounding one end of a first parallel circuit connecting a firstswitching element, a first damper diode, and a first resonance capacitorin parallel, connecting the other end of said first parallel circuit toone end of a second parallel circuit connecting a second switchingelement, a second damper diode, and a second resonance capacitor inparallel, and further connecting the connection point of said the otherend of said first parallel circuit and said one end of said secondparallel circuit to a direct-current power source through a primarywinding of a flyback transformer, grounding said the other end of saidsecond parallel circuit through a series circuit of a horizontaldeflection coil and an S-curve correction capacitor, grounding theconnection middle point of said horizontal deflection coil and S-curvecorrection capacitor through a parallel circuit of an intermediatepincushion distortion correction circuit and a horizontal linearitycorrection circuit, and installing switching element control means forswitching said first switching element by a horizontal drive signal, andcontrolling the OFF start timing and OFF period of said second switchingelement.
 2. A horizontal deflection circuit characterized by: groundingone end of a first parallel circuit connecting a first switchingelement, a first damper diode, and a first resonance capacitor inparallel, connecting the other end of said first parallel circuit to oneend of a second parallel circuit connecting a second switching element,a second damper diode, and a second resonance capacitor in parallel, andfurther connecting the connection point of said the other end of saidfirst parallel circuit and said one end of said second parallel circuitto a direct-current power source through a primary winding of a flybacktransformer, grounding said the other end of said second parallelcircuit through a series circuit of a horizontal deflection coil and anS-curve correction capacitor, installing switching element control meansfor switching said first switching element by a horizontal drive signal,and controlling the OFF start timing and OFF period of said secondswitching element, installing capacity varying means for varying thecapacity of said first resonance capacitor, and keeping constant thehigh voltage generated by said flyback transformer by varying thecapacity of said first resonance capacitor in a horizontal retraceinterval.
 3. The horizontal deflection circuit of claim 2, wherein saidcapacity varying means for varying the capacity of said first resonancecapacitor is controlled on the basis of the high voltage generated bysaid flyback transformer.
 4. The horizontal deflection circuit of claim2, wherein said capacity varying means for varying the capacity of saidfirst resonance capacitor is controlled so as to keep constant the pulsewidth generated in the horizontal retrace interval at both ends of saidresonance capacitor.